commit_tx: update HTLC-tx fees to match latest BOLT.

As per lightning-rfc BOLT #3 ec99f89:
"fixed htlc weight calculation"

Reported-by: Fabrice Drouin <fabrice.drouin@acinq.fr>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

lightningd/commit_tx.c

@@ -55,10 +55,10 @@ u64 htlc_timeout_fee(u64 feerate_per_kw)
 	 *
 	 * The fee for an HTLC-timeout transaction MUST BE calculated to match:
 	 *
-	 * 1. Multiply `feerate-per-kw` by 634 and divide by 1000 (rounding
+	 * 1. Multiply `feerate-per-kw` by 635 and divide by 1000 (rounding
 	 *    down).
 	 */
-	return feerate_per_kw * 634 / 1000;
+	return feerate_per_kw * 635 / 1000;
 }
 
 u64 htlc_success_fee(u64 feerate_per_kw)
@@ -67,10 +67,10 @@ u64 htlc_success_fee(u64 feerate_per_kw)
 	 *
 	 * The fee for an HTLC-success transaction MUST BE calculated to match:
 	 *
-	 * 1. Multiply `feerate-per-kw` by 671 and divide by 1000 (rounding
+	 * 1. Multiply `feerate-per-kw` by 673 and divide by 1000 (rounding
 	 *    down).
 	 */
-	return feerate_per_kw * 671 / 1000;
+	return feerate_per_kw * 673 / 1000;
 }
 
 static const struct htlc **untrimmed(const tal_t *ctx,

lightningd/test/run-commit_tx.c

@@ -10,6 +10,7 @@ static bool print_superverbose;
 #include <bitcoin/preimage.h>
 #include <bitcoin/privkey.h>
 #include <bitcoin/pubkey.h>
+#include <ccan/array_size/array_size.h>
 #include <ccan/str/hex/hex.h>
 #include <type_to_string.h>
 
@@ -317,22 +318,14 @@ static u64 increase(u64 feerate_per_kw)
 #else
 static u64 increase(u64 feerate_per_kw)
 {
-	switch (feerate_per_kw) {
-	case 0:
-		return 679;
-	case 679:
-		return 2169;
-	case 2169:
-		return 2295;
-	case 2295:
-		return 3873;
-	case 3873:
-		return 5150;
-	case 5150:
-		return 9651181;
-	default:
-		abort();
-	}
+	const u64 rates[] = { 0, 677, 2162, 2292, 3867, 5134, 9651181 };
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(rates); i++)
+		if (rates[i] == feerate_per_kw)
+			return rates[i+1];
+
+	abort();
 }
 #endif
 
@@ -715,7 +708,7 @@ int main(void)
 		       &x_remote_secretkey,
 		       &remotekey,
 		       &local_revocation_key,
-		       feerate_per_kw,
+		       feerate_per_kw-1,
 		       htlc_map);
 
 		printf("\n"